Since the advent of a resist for KrF excimer laser (248 nm), a pattern forming method utilizing chemical amplification is used so as to compensate for sensitivity reduction due to light absorption. For example, in the positive chemical amplification process, a photoacid generator contained in the exposed area is decomposed upon irradiation with light to generate an acid, an alkali-insoluble group contained in the photosensitive composition is, in the course of baking or the like after exposure (PEB: Post Exposure Bake), changed into an alkali-soluble group by the catalytic action of the generated acid and thereafter, development is performed using, for example, an alkali solution to remove the exposed area, whereby a desired pattern is obtained.
As for the alkali developer used in the method above, various alkali developers have been proposed. For example, an aqueous alkali developer of 2.38 mass % TMAH (an aqueous tetramethylammonium hydroxide solution) is being used as the alkali developer for general purposes.
In the positive chemical amplification process above, from the standpoint of, for example, enhancing dry etching resistance or enhancing pattern forming performance, attempts are made to let a group capable of decomposing by the action of an acid be provided in the polymer main chain through a polycyclic hydrocarbon group as a spacer (for example, Japanese Patent 3,390,702, JP-A-2008-58538 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), JP-A-2010-254639, JP-A-2010-256873 and JP-A-2000-122295).
With the miniaturization of a semiconductor device, the trend is moving toward a shorter wavelength of the exposure light source and a higher numerical aperture (higher NA) of the projection lens, and an exposure machine using an ArF excimer laser with a wavelength of 193 nm as a light source has been developed at present. As a technique to more increase the resolution, a method of filling a high refractive-index liquid (hereinafter, sometimes referred to as an “immersion liquid”) between the projection lens and the sample (that is, immersion method) has been proposed. Furthermore, EUV lithography of performing exposure to ultraviolet light having a shorter wavelength (13.5 nm) has been also proposed.
However, it is actually very difficult to find out an appropriate combination of a resist composition, a developer, a rinsing solution and the like, which is necessary to form a pattern having overall good performance.
In recent years, development of a pattern forming method using an organic solvent-containing developer is also proceeding (see, for example, JP-A-2008-292975 and JP-A-2010-197619). For example, JP-A-2008-292975 discloses a pattern forming method including a step of coating a substrate with a resist composition capable of increasing the solubility for an alkali developer and decreasing the solubility for an organic solvent developer upon irradiation with an actinic ray or radiation, an exposure step, and a step of performing development by using an organic solvent developer. According to this method, a high-definition fine pattern can be stably formed.
However, in the above-described pattern forming method, further improvements are demanded on roughness performance, uniformity of local pattern dimension, exposure latitude and prevention of film loss at the development.